Various packages are in use or have been proposed for containing a product, such as a food product or medical product, wherein the package is hermetically sealed until it is opened for use. One type of conventional package typically includes a cup or container comprising a hollow body having an opening or mouth surrounded by a flange to which a lid is heat sealed. While such packages function generally satisfactorily, it would be desirable to provide an improved package which could be more readily manufactured, which could be more easily used, and which would provide advantages and features not heretofore realized. For example, it is desirable to provide a container that can be opened readily and that can be used as a drinking glass.
Although packages comprising a cup and peel-away lid offer convenience of use, such packages are typically made from a relatively thin, thermoplastic sheet material. Such thin sheet material may be characterized as a web, film, sheet, sheet stock, etc., and such terms are used interchangeably herein. A conventional cup design or configuration incorporating a relatively thin sheet material may not provide the degree of strength and/or stability that is desired.
Such packaging also presents other problems. For example, the package may typically be filled with product at an elevated temperature. The elevated temperature may result from preparation of the product and/or from sterilization. In any event, the heated product may temporarily reduce the rigidity or strength of the package material (such as a thermoplastic sheet material), and the package material may tend to soften, and then deform or stretch under the weight of the product deposited within the package. This may cause the bottom of the package to bulge convexly (i.e., downwardly or outwardly). When the package ultimately cools, the convex shape at the bottom of the package may remain, thereby creating a somewhat unstable support base for the package.
Such deformed package bottoms are sometimes referred to as "rocker bottoms." A package with such a "rocker bottom" may tend to more easily tip over rather than sit flat on a table top or other flat, horizontal surface. Consequently, it would be desirable to provide an improved, low-cost package that can be processed at high speed and that, when filled with product at an elevated temperature, will have no tendency, or only a minimal tendency, to develop a "rocker bottom" or other undesirable deformation.
Packages are typically subjected to external loads during manufacturing, distribution, storage, and use. For example, packages may be stacked one on top of the other. Hermetically sealed packages fabricated from thin sheet stock or film typically do not exhibit particularly high resistance to stacking loads. Accordingly, it would be desirable to provide a package of that type having increased compression strength so as to accommodate stacking loads without crushing a corner or other portion of the package.
Such a stronger package should not, however, require excessively thick materials. Rather, such an improved package should accommodate fabrication from relatively thin sheet stock so as to permit the overall manufacturing cost to be kept low and consistent with the desirability of providing a one-time use, disposable package.
Some products which are contained within hermetically sealed packages may be deleteriously affected by certain packaging materials. For example, some packaging materials may permit an undesirable amount of ambient atmospheric substances (e.g., oxygen, water vapor, etc.) to migrate through the package into the product contained therein. This may be a significant problem for packaged products which are intended to have long shelf lives. Accordingly, it would be beneficial to provide an improved sheet material for use in forming a package or portion thereof (e.g., the cup portion of a package) which would have the desired barrier properties relative to the ambient atmosphere during long-term storage. Preferably, such an improved packaging sheet material should also be thin enough to accommodate high-speed, low-cost manufacturing of a disposable package.
Such an improved sheet material should also provide improved column strength, scratch resistance, impact strength, and superior aesthetic appearance.
Such an improved sheet material should also desirably accommodate its formation into a package body, container, or cup which is suitable for being heat-sealed with a film lid. Further, the package should preferably have a strong, hermetic, heat seal between the lid and cup which can be created with high-speed manufacturing techniques and which permits the lid to be easily removed by the user when the user desires to open the package. Further, such an improved heat seal of the lid to the cup should accommodate the optional incorporation of a lift-up tab or pull-up tab in the lid if desired.
Preferably, the improved heat seal between the package lid and package cup should also accommodate manufacturing processes wherein rows of cups and lids are heat-sealed together from a continuous web of lid material and a continuous web of cup material. The heat seal should accommodate subsequent punching or separation of the individual, sealed packages from the two continuous webs with the resulting, individual packages having a few or no rough edges or stringy, "hair-like" strands, etc., around the periphery. In this respect, the improved package body or cup material, as well as the lid material, should accommodate the severing of the individual packages from the continuous webs of material in a way which will minimize, if not substantially eliminate, rough edges or hair-like filaments and strands of material about the periphery of the package. This is especially important where the package is used for a liquid food product which is intended to be drunk directly from the package cup after removing the package lid. In such applications, it is most desirable to provide a drinking edge which is clean and smooth.
Some types of conventional package cups and hermetically sealed lids are fabricated, respectively, from a moving web of cup material and an overlying moving web of lid material which has a composition that differs from the composition of the cup material. The cup material is typically a type of thermoplastic which can be readily punched out of the web and which has a sufficient thickness and stiffness to accommodate the punching of the package in a way that leaves a relatively smooth, non-stringy periphery. While such packages generally function satisfactorily, it would be desirable to provide an improved package design that could accommodate manufacture of the package cup portion from a thinner web of material and/or from other materials which are difficult to smoothly punch, such as polypropylene. The use of these other materials, such as polypropylene, for example, can provide improved, or more desirable, properties with respect to the following: barrier characteristics, compatibility with various products, stability over an extended shelf life, resistance to degradation from ultraviolet energy, tolerance to thermal energy, and heat-seal formation with certain types of lid materials.
Some types of packaging materials are more easily processed or formed into package bodies or cups than are other types of materials. With some types of materials, the manufacturing process must be very tightly controlled with respect to temperatures, formation forces, etc., compared to using other types of packaging materials which can accommodate a greater latitude of processing parameters. However, in some applications certain types of materials which are difficult to process may nevertheless be preferred owing to improved packaging characteristics (e.g., strength). Thus, it would be desirable to provide an improved method and apparatus for forming package bodies or containers from such types of materials, but at high speed and with a reduced product reject rate.
In particular, it would be desirable to provide an improved process and apparatus for heating the web of material so that it can be thermoformed into the package body or cup. Such an improved process and apparatus should tolerate minor misalignment of the thermoforming apparatus and web in both the machine web feeding direction and the transverse or cross direction. The process and apparatus for heating the web should be effective to rapidly and effectively heat the material in a controlled manner so that the final temperature is within a desired range at each container-forming location across width of the web.
Additionally, the improved process and apparatus should permit the high-speed formation of the body or cup portion of the package in a way that results in the creation of the desired configuration and thickness of the wall as may be necessary to provide the desired strength and stability characteristics of the package. Such processes and apparatus should function at high speed, in aseptic environments, and in a reliable manner with a minimum product reject rate.
The present invention provides an improved multi-ply sheet for a container and also provides a package comprising a container with a hermetically sealed lid having the above-discussed benefits and features. Another aspect of the present invention includes an improved method and apparatus for making the container and hermetically sealed package which can accommodate designs having the above-discussed benefits and features.